UPDATE

Six men have been hospitalized following a "serious accident" during a clinical trial for a pain killer at a laboratory in Rennes, western France, the country's health ministry said in a statement Friday.

One of the six who have been hospitalized has been declared brain dead, and three others are now reported to have brain damage that scientist Gilles Edan says may be "irreversible," according to the Associated Press.

Speaking at a press conference in Rennes, Edan said that the fifth patient is suffering neurological problems, and the sixth's symptoms are not severe.

The patients, who entered the study as volunteers, are all males aged 28-49 years old, the AP reported. They were all considered healthy before the trial began.

According to France's health minister, 90 people total participated in the lab test. The 83 who have not been hospitalized have been contacted, the AP reported.

Edan said that there is "no known antidote" to the drug, according to the Associated Press.

The test was conducted in the Biotrial laboratory in Rennes, who released a statement Friday afternoon local time saying that "serious adverse affects related to the test drug" had occurred during the trial.